1. Field of the Invention
The present invention relates to a semiconductor, and a functional device including the semiconductor (e.g., a cell, a capacitor, a sensor, a photoelectric transducer, a photoelectrochemical cell, a recording device, an electrochromic device, etc.). More specifically, the present invention relates to a semiconductor having a specific compound adsorbed on a surface thereof to control a flat band potential (Vfb), and a functional device including the semiconductor.
Particularly, concerning the electrochromic device, the present invention relates to an optical device which includes an electromotive force-generating element for generating electromotive force corresponding to the intensity of an electromagnetic wave and an electrochromic device, and an image-taking unit including the optical device.
2. Description of the Related Art
In many cases, the performance of functional devices, such as batteries, capacitors, sensors, photoelectric transducers, photoelectrochemical cells, recording devices, electrochromic devices, and the like, depends on a reaction with a functional material which takes place on a semiconductor surface. The specification of U.S. Pat. No. 4,927,721 and JP-A No. 1-220380 describe typical examples of dye sensitizing photoelectric transducers, and the specifications of U.S. Pat. Nos. 6,067,184, 6,426,827, 6,605,239 and 673,405 and JP-A No. 2003-511837 describe typical examples of electrochromic devices. For a reaction on a semiconductor surface, the flat band potential of the semiconductor material is important. A reason for this is that, when the semiconductor material and the functional material donate/accept electrons at a semiconductor interface, the electrons pass through a valence band edge (i.e., a flat band potential) of the semiconductor material.
It is known that the flat band potential of a semiconductor material is inherent in the semiconductor material, and may vary depending on pH (see, for example, Hiroshi Tubomura, Photoelectrochemistry and Energy Conversion, published by Tokyo Kagaku Dojin, and S. Roy Morrison, Electrochemistry at Semiconductor and Oxidized Metal Electrodes, published by Plenum Press). However, the flat band potential is not necessarily sufficiently controlled.
Although the flat band potential can be controlled through selection of semiconductor materials, any expensive and/or dangerous semiconductor materials cannot be used even if the flat band potential thereof is suitable and expected to enhance the performance of the functional device. On the contrary, even when the semiconductor material is safe and stable and can be produced at relatively low cost, the effect that is to be achieved by the functional device is low unless the flat band potential is at a suitable level. There has been a demand for a method of controlling the flat band potential of a semiconductor material independently from the semiconductor material.
Although pH-based control is available, an organic solvent is often used for the functional device due to functional limitations, and therefore, control methods other than the pH-based control have been desired.
Regarding the dye sensitizing photoelectric transducers, it has been reported that using an electrolyte containing a pyridine compound reduces a reverse current, increasing an open circuit voltage, as disclosed in JP-A No. 2004-47229, JP-A No. 2004-171821 and JP-A No. 2004-273272. However, the reverse current is not necessarily sufficiently prevented, and therefore, there is a demand for means of preventing the reverse current to a further extent. As is apparent from the example of the dye sensitizing photoelectric transducers, there is a demand for general-purpose means of controlling the semiconductor flat band potential, which can be applied to general functional materials including a semiconductor, and a device in which a semiconductor flat band potential is controlled.